most games don't make use nor take advantage of multiple GPUs yet. I believe Crysis is one of those game that doesn't support multiple GPUs. It's a pretty old game. Crysis 3 was built to run on multiple GPUs however. Test it on the beta.

it seems to work a bit better on the 32 bit version than the 64 bit version and i suppose my processor could be holding it back a bit, maybe a little bottleneck on my cards. and like you said the optimization might not be that great.

The only reason I could see you getting worse performance is you're running out of VRAM. This was an issue I was having with my SLI GTX 460s. It could just be a CPU bottleneck though. Do you have the Rygels Texture pack? It might help if you created a RAM disk and put the texture files on the RAM disk and then create a symbolic link to them. This worked with one of my friends and he had a gtx 570 which has about 1.2GB of VRAM.